The aim of the present work was to perform a morphofunctional analysis of the effects of total sleep deprivation of different durations on neuron and synapse ultrastructure in the somnogenic formations (layers III-V of the anterior limbic cortex, field CA1 of the dorsal hippocampus, the pontine reticular formation, the dorsal cervical nucleus, and the locus ceruleus) in rats, with assessment of study investigative, comfort, and sexual behavior, as well as food and water consumption. Reparative changes in neurons and synapses after total sleep deprivation lasting 12-24 h were accompanied by increases in all types of behavioral reactions. Repair processes in neurons and synapses were somewhat weakened after total sleep deprivation lasting 36 h, while dystrophic changes affected greater proportions of neurons and synapses, and the numbers of behavioral reactions decreased.